public class test04 {
    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode() {}
     *     TreeNode(int val) { this.val = val; }
     *     TreeNode(int val, TreeNode left, TreeNode right) {
     *         this.val = val;
     *         this.left = left;
     *         this.right = right;
     *     }
     * }
     */
        public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
            //用递归最简单！
            if(root1==null){
                return root2;
            }
            if(root2==null){
                return root1;
            }
            TreeNode root = new TreeNode(root1.val+root2.val);
            root.left = mergeTrees(root1.left,root2.left);
            root.right = mergeTrees(root1.right,root2.right);
            return root;
        }
}
